Kharjo

After aquiring Kharjo as a follower, by doing his quest, if you decide to split ways he will say something along the lines of "heading home" and after this it can be quite difficult to find him again. The easiest way to find him again is to wait at the small camp next to Riften Stables. If you keep waiting for 6-12 hours at a time, he will show up after a few days at the most.